Goodwill and Other Intangible Assets - Gross Carrying Amount, Accumulated Amortization And Net Carrying Amount Of Other Intangible Assets (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 3,450	$ 3,497
Accumulated Amortization	(1,950)	(1,884)
Net Carrying Amount	1,500	1,613	$ 1,750
Client relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	2,633	2,669
Accumulated Amortization	(1,521)	(1,470)
Net Carrying Amount	1,112	1,199
Core deposits
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	681	686
Accumulated Amortization	(335)	(320)
Net Carrying Amount	346	366
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	136	142
Accumulated Amortization	(94)	(94)
Net Carrying Amount	$ 42	$ 48